And thats exactily what the trait does. Your ruler won't die (at least not from old age, didn't try my luck making him a general). Keep in mind, this costs 800 points in the nation creator, and even after other trade-offs you will have to pick a 800 point custom nation to create a immortal 6/6/6 ruler and won't have much to spend on ideas and development...
Edit: And thats also the only way to gain this trait, you cannot get it in your normal games...
